The present invention relates to a filtering device, especially a suction return filter, having a filter housing which includes two utility connections and a tank connection. The filter housing serves as a holder of at least one filter element, and is provided with three non-return valves. Two of the non-return valves are maintained in closed settings under spring bias.
In known filtering devices that are presently commercially available, the return valves are mounted at different points on the filter housing, and consequently, take up considerable structural space thereon. Futhermore, this arrangement increases the outlay for construction of the filtering device and raises its overall cost. Known solutions provide that primary filtered fluid can be fed to the user connected by a utility connection. The known suction return filters are provided primarily for use in the tank connection for an oil container. The filter housing and the utility and tank connections are designed such that they can withstand pressure peaks without damage. Use of a return valve guarantees that when a pressure peak occurs in the tank connection, and consequently in the tank or oil container, the resulting peak can be deconstructed by discharge in the direction of at least one of the utility connections.
DE 195 16 657 A1 discloses a filtering device for a telescopic-hydraulic cylinder of simple operation for raising and lowering a load surface or a loading platform or the like in or on trucks. One spring-loaded return valve is arranged in a bypass line to the filter element, while another spring-loaded return valve is connected to the rear of the bypass branch and the filter element. These spring-loaded return valves, together in one modular unit, facilitate the driving of the hydraulic cylinder with unfiltered fluid passing through the bypass. With the lowering or displacement of the hydraulic cylinder, the fluid moving in the direction of a collection container is filtered by the filter element, whereby the return valve in the bypass line is closed. Another, not spring-loaded return valve between a hydraulic pump and a valve arrangement for the control of the filter element protects against overload of the hydraulic pump in the case of an undesired reversal of the flow of the fluid. In another embodiment, a comparable arrangement includes a spring-loaded return valve in the bypass and two return valves having no spring load, one of them in another bypass line and one of them in the direct feed to the filtering element. The return valves, fitted within the filtering device as independent modular parts, likewise take up considerable structural space. With disruptions of the operation, exchange of the return valve is possible only with great difficulty.
A filtering device disclosed in DE 195 15 962 A1 serves in supplying a hydraulic user with hydraulic liquid. The associated hydraulic connection includes a tank connection for a supply tank, a hydraulic pump for making available the hydraulic liquid and a return filter, through which the hydraulic liquid flowing back from the hydraulic user is filtered. The leading edge of the return filter is connected through a line with the tank for the hydraulic liquid. A non-parallel connection includes a pressure limiting valve and a retrofitted suction valve and ends beneath the hydraulic liquid level of the supply tank. These two valves are spring-loaded return valves, the same as another spring-loaded return valve arranged between tank and filter element. The three spring-loaded return valves, as independent structural parts, form no interdependent modular unit, hut rather produce a hydraulic emergency supply for the user. The spring-loaded return valves in this case are mounted at different points and separated from one another on a part of the filtering device. This solution also embodies a large construction. Since the return valves are to be controlled hydraulically at different points, disruptions of the operation during operation of the device cannot be totally excluded.
Objects of the present invention are to provide an improved filtering device which is of low-cost construction and remains operationally reliable during operation.
According to the present invention, all of the return valves are arranged together as one modular unit at one end of the filter housing. The return valve opens in a direction counter to this and is in the form of an integral component part of one of the spring-loaded return valves. A compact arrangement of the entire return valve unit is possible and can be mounted in a constructively simple manner at a central point on the filter housing. This arrangement also simplifies the exchange of the modular unit for another modular unit, when an unexpected breakdown of any one of the return valves occurs.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.